Ultra‐Sensitive and Low Dose Rate Compatible X‐Ray Detector Based on Centimeter‐Size (FACs)PbBr ₃ /CsPbBr ₃ Single Crystal Heterojunction

Three‐dimensional (3D) metal halide perovskites (MHPs) show great potential as direct X‐ray detection materials. However, these materials suffer from high dark currents, severe ion migration, and incompatibility with ultra‐high sensitivity and ultra‐low detection limits, hindering their applications. In here, we present an in situ liquid‐phase epitaxial growth method for 3D (FACs)PbBr 3 single crystal (SC) films on 3D CsPbBr 3 SC substrates, successfully constructing a highly transparent (FACs)PbBr 3 /CsPbBr 3 heterostructure SC with an area of 15 × 17 mm 2 . The lifetime of the (FACs)PbBr 3 SC film surprisingly increases to 897 ns, and the trap‐state density ( n trap ) is suppressed to 1.46 × 10 9 cm −3 . The connection of (FACs)PbBr 3 SC film and CsPbBr 3 SC substrate creates a p‐n junction at the interface, greatly decreasing the dark current to ∼10 nA at high reverse bias of −300 V. For 120 keV X‐ray photons, a simple symmetric Au/(FACs)PbBr 3 /CsPbBr 3 /Au SC detector showcases ultra‐high sensitivity of 5.19 × 10 5 µC Gy −1 cm −2 and incredibly low detection limits of 0.8 nGy s −1 . Notably, it enables self‐driven detection with a sensitivity of 644 µC Gy −1 cm −2 . This work provides a simple strategy for suppressing the dark currents in 3D MHPs SC and realizes the outstanding balanced performances for hard X‐ray detectors.